Valley Fever is caused by a fungus
Most people think of mold spores coming from that damp spot underneath your sink–or a container of moldy food left in the fridge. However, soil is actually a big reservoir of mold, and surprisingly, it doesn’t have to be moist soil. The fungus Coccidioides is responsible for a disease called Valley Fever, also called San Joaquin Valley Fever, or Coccidioides. This type of mold is found in two species, C. immitis and Coccidioides posadasii. C. immitis is found in California, while C. posadasii is found in other US states and other parts of the world, especially arid deserts with high salt content.
The two species of Coccidioides fungus grow in the soil and infect people and animals the same way. They exist as mycelia (the network of thread-like structures called hyphae) in the soil, branching and elongating like other molds. After only 1 week of growing, some of the cells start to die while others remain live but experience thinning of the cell walls. The dead cells break apart to act as “wings” and help the live cells to float and move on air currents. These are called arthroconidia and act as spores. When animals and people disturb soil containing Coccidioides fungus, these spores are propelled into the air and can be inhaled. They are the perfect length (2-5 nm) to be carried deep into the lungs to the terminal bronchioles, which is where the air pathways branch into respiratory pathways (leading to the small sacs called alveoli). Once the spores are in the lungs, they undergo transformation into spherical bodies “spherules” by shedding the outer layer of the arthroconidia.
The spherules grow to a size of 75 microns in diameter. The spherules divide internally by developing internal septae, which divide the spherule into compartments. Each compartment has endospores. As the spherule impregnated with endospores grows, it eventually ruptures and releases the endospores in the region, including the alveolar sacs. The local release of endospores causes host response, and acute inflammation ensues. The endospores can further multiply within tissues and, when released in the environment, can lead to mycelial growth. (Coccidioidomycosis)
When the endospores are released and the host becomes infected, infection can remain local or more in immuno-compromised people, travel to other areas of the body. The alveolar macrophages (our bodies’ immune cells in the lungs) pick up these endospores and may carry them to vertebrae, joints, and the central nervous system (which can be deadly). Even if the infection remains in the lungs, symptoms like painful skin nodules, skin lesions, fever and weight loss are common manifestations of the disease.
There are complicating factors that make Coccidioidomycosis difficult to diagnose. About 60% of the people who inhale spores which remain in the body do not show symptoms (asymptomatic). In addition, presentation and symptoms can be similar to tuberculosis. Areas of commonality for these 2 diseases overlap geographically, patients can develop chronic, necrotizing lesions that clinically & pathologically resembles tuberculosis, and individuals can be infected with both diseases at the same time (coinfection). It can also cause flu-like symptoms, which can persist for weeks or even months. Once diagnosed properly, doctors take different approaches to treatment of Coccidioidomycosis. In healthy individuals, often only supportive care and monitoring with chest x-rays is needed. In immunocompromised individuals, there are a variety of antifungal medications available. If the disease reaches the central nervous system, often treatment is continued indefinitely or for life due to the risk of resurgence or progression of the disease.
Scientists have been studying the seasonal patterns of precipitation that allow the fungus to grow more in some years than others, and have formulated a “grow and blow” hypothesis. Specifically, a dry foresummer or fall kills other microorganisms that might compete with Coccidioides. Subsequently, winter rainfall leads to spore formation in the soil, which are released whenever the soil dries out again. If summer is more wet than normal, this has been shown to lower cases of Valley Fever. (Relating coccidioidomycosis (valley fever) incidence to soil moisture conditions) The fungus is most prevalent in the top 2-12 inches of soil.
Who is at risk of getting Valley Fever? Construction workers, agricultural workers, wildland firefighters, military personnel, workers in mining, quarrying, gas and oil extraction jobs and archeologists are more likely to disturb the soil and breathe it in, but it can also be present in the air after a natural disaster like a dust storm or earthquake. For example, In October 2007, a construction crew excavated a trench for a new water pipe. Within three weeks, 10 of 12 crew members developed coccidioidomycosis (Valley Fever), an illness with pneumonia and flu-like symptoms. Seven of the 10 had abnormal chest x-rays, four had rashes, and one had an infection that had spread beyond his lungs and affected his skin. Over the next few months, the 10 ill crew members missed at least 1660 hours of work and two workers were on disability for at least five months. (Preventing Work-Related Coccidioidomycosis (Valley Fever)) Unfortunately, there is no reliable way to test the soil for spores before working in a particular place. Therefore, people living and working in the area where Valley Fever exists should be aware and take precautions. Most of these precautions involve avoidance of the dust by wetting soil down, suspending activity during high winds or dust storms, and remaining upwind or in air conditioned vehicles using HEPA air filters, but when this is not possible, workers need to wear approved respirators, not just loose-fitting “dust” masks. In addition, workers need to clean themselves, their clothing and equipment after working in order to prevent transportation of the fungus to other areas. For specific actions to reduce contracting the disease, this fact sheet is really helpful. Thankfully, it’s not contagious from person to person because the endospores do not transmit, but lab workers who are handling soil samples need to be especially careful because the spores which are propagated from dry soil can be inhaled easily. If you live in an area where Valley Fever is prevalent, protect immunocompromised people, children and older people by helping them to avoid dusty air and stay inside and use HEPA air filters when it’s dusty outside.
Photo by Matthieu Joannon on Unsplash
